Hi i'm searching for good headphones that let me play well flac music and some movies i saw these two and i'd like to hear your opinion, because i don't know almost anything about headphones.
Both are good headphones in their own way. Sennheiser HD598 are probably more neutral and refined with bigger soundstage, but being open back headphones they don't provide any isolation. Sony MDR 1R on the other hand are closed back headphones intended for portability, so they provide isolation and don't leak sound.
Closed back headphones often provide punchier bass.
Not a lot. Some headphones need some extra ampliciation to sound good, but both HD598 and MDR 1R can be properly driven without extra amplification. That said, getting a good quality amp and dac (Fiio E10 for desktop use or Fiio E07K/E17 for desktop and portable use) and listening to high quality recordings (not only high quality files) you can get the best of your headphones.
Recording quality is very important if you want to get the best out of your headphones.